Scanner wedge mode (#437)

* Add code_scan_listener package

* Implement wedge controller widget

* Update barcode settings widget

- Allow user to choose which barcode scanner to use

* Fix typo

* Select barcode scanner widget based on user preference

* Fix rendering issues for wedge controller

* Update release notes

* Add unit test for wedge scanner widget

- Required some tweaks to other code

* Use better library

- https://github.com/fuadreza/flutter_barcode_listener
- Fork of https://github.com/shaxxx/flutter_barcode_listener
- Properly handles key "case" issues (shift, essentially)
- Verified that it works correctly for multiple character types

* Local copy of code, rather than relying on package which is not available on pub.dev

* Fix unit test

lib/preferences.dart

@@ -40,6 +40,11 @@ const String INV_STRICT_HTTPS = "strictHttps";
 
 // Barcode settings
 const String INV_BARCODE_SCAN_DELAY = "barcodeScanDelay";
+const String INV_BARCODE_SCAN_TYPE = "barcodeScanType";
+
+// Barcode scanner types
+const int BARCODE_CONTROLLER_CAMERA = 0;
+const int BARCODE_CONTROLLER_WEDGE = 1;
 
 /*
  * Class for storing InvenTree preferences in a NoSql DB